The subject of the present invention is a nutrient composition resulting from maize steeping.
It also relates to the process for producing such a composition, as well as its application as culture medium in fermentation industries and as food or food additive in compositions intended for humans or animals.
Maize steeping constitutes the first stage in the extraction of starch in wet milling. It consists in maintaining the maize placed in silos for a given time in hot water containing a small quantity of sulphur dioxide in order to facilitate subsequent protein-cellulose-starch separation and to prevent, moreover, the growth of undesirable microorganisms.
During this operation, two essential phenomena occur simultaneously. On the one hand, the highly fermentable soluble matter contained in the maize grains are transferred into the steepwater. Moreover, the steeping conditions (presence of sulphites and reducing sugars, and the temperature level) are favourable to the rapid development of mainly lactic acid bacteria.
The main advantage of the steepwater, commonly called corn steep by persons skilled in the art is linked to their composition in relation to essential compounds which are derived from the transfer of this soluble matter. These compounds constitute factors which are favourable to the growth of the microorganisms and to the production of secondary metabolites, and they make steepwater an ideal source of nutrients in the fermentation industry.
Indeed, corn steep contains as easily assimilable carbon sources: sugars and organic acids, as nitrogen and carbon sources: amino acids and polypeptides and as sources of trace elements necessary for the growth of microorganisms: "buffering" agents and minerals.
In addition, it constitutes a relatively inexpensive substrate, compared with yeast extracts which represent the reference material in this field, and which are also used as animal and human food.
Moreover, it is known that the use of corn steep as replacement for complex nitrogen sources such as cotton or soya bean proteins makes it possible to substantially increase antibiotic production yields.
For use in fermentation, corn steep should be subjected beforehand to sterilization, of which the temperature and pH conditions as well as the duration are chosen so as to obtain the destruction of microorganisms.
Thus, the temperature is generally between 105.degree. and 130.degree. C. and the pH varies between 3.0 and 8.0. Now, these temperature and pH conditions cause the precipitation of certain constituents of corn steep, which causes numerous disadvantages.
Indeed, the use of such a nonhomogeneous corn steep poses a problem as regards its preparation, and in particular during its concentration. In addition, its use causes the formation of a large deposit on the walls of fermenters, which deposit risks blocking the temperature exchangers. Finally, the recovery of the fermentation products may be substantially disrupted following the blocking of the membranes and of the filters.
Among the solutions proposed to solve this problem, the oldest is that which consists in extracting from the corn steep, by chemical precipitation, the substances responsible for coagulation. Thus, the addition to corn steep of alkaline agents (calcium hydroxide, sodium hydroxide and the like) or of metallic compounds (especially aluminium salts), in order to cause the precipitation of certain proteins, sulphite or sulphate compounds or alternatively phytic acid, is known. However, in addition to the extra cost associated with this additional treatment, its major disadvantage is the removal of nutrients from the medium. Furthermore, such a treatment requires the introduction, into the corn steep, of chemical products in quantities which may be high, which considerably modifies its composition and thus limits its potential uses.
Ultrafiltration has also been used to separate from the maize steepwater the molecular species, especially proteins and peptides, which are heat-coagulable. This technique has in fact been the subject of a French patent No. 2,140,672 granted to the company SCHOLTEN-HONIG RESEARCH.
Finally, it has more recently been proposed to treat corn steep with enzymes.
Thus, U.S. Pat. No. 4,914,029 granted to the company DORR-OLIVER describes a treatment with a phytase-cellulase mixture.
However, while such a treatment makes it possible to avoid the precipitation of phytic acid, it is not sufficient to solve completely the problem of the formation of a precipitate during the sterilization of corn steep.
Moreover, a treatment with a protease is described in Japanese patent No. 04-198,080 filed by the company MITSUI TOATSU CHEMICALS: the action of such an enzyme on a corn steep contributes to the improvement of its filterability. Corn steep thus treated is intended for the preparation of a liquid fertilizer.
Likewise, M. ROUSHDI, Y. GHALI and A. HASSANEAN have studied the action of two proteolytic enzymes (Alcalase and Neutrase manufactured by the company NOVO) on maize steepwater in order to reduce the duration of the steeping operation and to obtain a starch having a reduced protein content.
However, it appeared that a treatment of corn steep with a proteolytic enzyme was not sufficient to satisfactorily eliminate the problems mentioned above.
Consequently, none of the treatments described and used up until now has made it possible to solve satisfactorily the problem posed by the formation of a precipitate during the sterilization of corn steep, that is to say without causing the loss of a substantial fraction of the constituents of corn steep.